RegisterSDKHandlerClient registers the http handlers for service SDK
to "mux". The handlers forward requests to the grpc endpoint over the given implementation of "SDKClient".
Note: the gRPC framework executes interceptors within the gRPC handler. If the passed in "SDKClient"
doesn't go through the normal gRPC flow (creating a gRPC client etc.) then it will be up to the passed in
"SDKClient" to call the correct interceptors.